Vletti'azan'uosus
As the replies show, Csilla was destroyed by
The Brotherhood of The Maw.
However most probably don't tell you about the aftermath. The Maw was instantly enemy number one, replacing The Bryn'adul and Sith Empire, which both had fallen or were falling around that time.
The destruction left many Chiss homeless and led to an influx of refugees. Many refugees joined
The Elysium Empire rather than
The Galactic Alliance, possibly comparing it to The First Order, which had once been close with Csilla, but had fallen as well. The Elysium Empire is ready to join the fight against The Maw soon, since three of its' most prominent admirals are from Csilla (
Grand Shepherd Burtch
Thaliias
Keatoch
), but it has stayed out of the conflict so far, letting The Galactic Alliance handle the majority of the fighting.